1. Technical Field
This disclosure relates to aerodynamic control surfaces of aircraft in general, and more particularly, to systems and methods for detecting aircraft leading-edge wing slat skew.
2. Related Art
Slats are aerodynamic surfaces on the leading edges of the wings of fixed-wing aircraft that, when extended, enable the wing to operate at a higher angle of attack and/or a slower speed without stalling. A higher coefficient of lift is produced as a result of angle of attack and air speed so that, by extending its slats, an aircraft can fly at slower speeds, and/or take off and land within shorter distances. Slats are usually used while landing or performing other low-speed maneuvers that are close to the aircraft's stall speed, but are usually retracted during normal, high-speed flight so as to minimize their aerodynamic drag.
Modern slats are installed at the leading edges of an aircraft's wings in bilaterally symmetrical pairs, and during operation, are all extended and retracted simultaneously with each other. However, certain failures of the structural members or the drives of the slats of some types of modern aircraft can result in a condition referred to as “skew,” in which one end of the slat becomes stuck or decoupled from the associated slat drive mechanism during extension or retraction, thereby allowing that end of the slat to become displaced relative to those of the other slats. Due to the stiffness of the slats, this creates only relatively small deflections when aerodynamic loads are applied to that slat during flight. However, if this type of failure goes undetected, the slat can become completely disconnected from the aircraft wing, resulting in the loss of the slat, and potentially, a more serious type of failure.
In particular, the loss during flight of slats that are located more outboard on the wing of an aircraft, while aerodynamically undesirable, is not deemed as serious as the loss of the slats located more inboard on the wing, because the former are typically smaller, and will simply fly harmlessly rearward in the slipstream of the aircraft, whereas, the latter, which are typically larger, heavier and located more toward the centerline of the aircraft, could collide with and damage the empennage, i.e., the rudder and/or elevators, of the aircraft, thereby resulting in a more serious loss of aircraft control.
Some modern commercial jet aircraft typically incorporate two bilaterally symmetrical wing-mounted engines, with one pair of slats being mounted inboard of the engines and six pairs of slats being mounted outboard of the engines. For the foregoing reasons and others relating to skew detector size and cost, conventional slat skew detection systems typically ignore the smaller, most outboard pair of slats, and detect skew in all of the remaining slats, except for the outboard ends of the pair of slats located immediately inboard of the most outboard pair, and the inboard ends of the pair of slats located immediately outboard of the engines.
Accordingly, what is needed are systems and methods for detecting skew of an aircraft wing slat regardless of its size or location within the wing, and for doing so reliably and without adding significant weight or cost to the aircraft.